The long-term aim of this research project is to gain a better understanding of the involvement of defined T- cell subpopulations in the establishment of protective and/or pathogenic immune responses in human Chagas'disease, a prevalent and endemic parasitic disease caused by the infection with Trypanosoma cruzi. Through a series of comprehensive mechanistic studies we will dissect the role of CD4+ and CD8+ T cells with differential expression of CD28 in the dynamics of the immune response in human Chagas'disease. Specific aims are: 1.Determine the adhesion molecule expression by CD28+ and CD28- T cells from individuals with different clinical forms of Chagas'disease;2. Determine the intensity and specificity of the cytotoxic function of CD28+ and CD28- T cells from individuals with different clinical forms of Chagas'disease;3. Determine the regulatory function of CD28+ and CD28- T cells from individuals with different clinical forms of Chagas'disease. To perform these studies we will use peripheral blood mononuclear cells from a selected group of chagasic patients, carefully classified as belonging to the indeterminate or severe cardiac clinical forms. Cellular recruitment potential, cytotoxicity and regulatory functions will be evaluated ex vivo and after in vitro stimulation with parasite, as well as autologous antigens, through the analysis of expression of surface or intracellular molecules by FACS and by biological assays. These studies will greatly improve the knowledge on Chagas'disease immunopathology by clarifying how CD28+ and CD28- sub- populations relate to the differential clinical evolution of disease. We hope that the new concepts derived from our findings will allow for the identification of markers of disease evolution and/or morbidity, offering new possibilities of clinical intervention to benefit the 17 million infected people. Transcending the limits of Chagas'disease, our findings will add to our knowledge on the biology of human T cells with differential expression of CD28, opening new possibilities of studies in other human diseases. Finally, depending largely on a Brazilian scientific core of researchers and students, the implementation of these studies will also lead to increased research capacities in Brazil through intense collaborations with international and national specialists.